Electrical generator with ferrofluid bearings

ABSTRACT

An electrical generator includes a magnet constrained to move relative to a conductor by a support structure, with a ferrofluid bearing providing an ultra low friction interface between the magnet and support structure. The assembly has a critical angle of displacement from a horizontal static position of less than 1 degree, and preferably less than 10 minutes. An electrical signal is generated in the conductor by the moving magnetic field.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] This invention relates to the generation of electrical energy bythe movement of a magnet within a coil, and more particularly to anultra low friction bearing for the magnet.

[0003]2. Description of the Related Art

[0004] Moving a magnet through a conductive coil induces anelectromotive force that generates a current in the coil. If the magnetis moved back and forth in a reciprocating motion, the direction ofcurrent flow in the coil will be reversed for each successive traverse,yielding an AC current.

[0005] Several electrical generating systems have been developed thatmake use of reciprocating magnet movement through one or more coils. Forexample, in U.S. Pat. No. 4,260,901, wave motion in a body of watercauses a float to move up and down, which in turn imparts areciprocating motion to a magnet that travels between a pair of coilsstationed at opposite ends of its path. In U.S. Pat. No. 5,347,186, arare earth magnet and a coil are positioned to move linearly back andforth relative to each other. The magnet can either be fixed and thecoil moved up and down relative to the magnet, as by wave action, thecoil fixed and the magnet moved relative to the coil as by pneumaticpressure, or the coil housing shaken or vibrated, as by being carried bya jogger, to cause a reciprocating motion of a magnet which moves withinthe coil. In U.S. Pat. No. 5,818,132, a moving magnet is confined to abi-directional linear or near linear motion through each of at least twomutually spaced coils for providing power in applications such as longlife flashlights, alarms systems, communication devices located atplaces where conventional electric power sources are unavailable, andrelatively high power repetitive forces such as the forces on the heelof a shoe during walking or running.

[0006] In each of these applications it is necessary to either hold themagnet or coil stationary and forcefully move the other component, orapply a vigorous shaking or vibrating motion to a housing for theassembly so that the magnet moves relative to the coil. This makes thedevices unsuitable for applications in which only a gentle actuatingforce is available to move the housing, particularly if the movement isin a generally horizontal direction. Thus, in the example of a hand heldflashlight with a magnet and coil assembly for supplying power to thebulb, simply holding the flashlight in the user's hand while walking sothat it moves in a shallow, generally horizontal arc corresponding tothe user's hand motion, may be insufficient to cause adequate motion ofthe magnet relative to the housing.

SUMMARY OF THE INVENTION

[0007] The present invention seeks to provide a new electrical generatorsystem and method in which frictional forces between a magnet andsupport structure are so low that relative movement between the magnetand a proximate conductive coil is sufficient for useful electricalpower generation, even if the movement is horizontal and only a slightmovement is imparted to the support structure.

[0008] These goals are achieved with an electrical generator in which amagnet is arranged to move relative to a support structure, the assemblyhaving a critical angle of displacement from a horizontal staticposition of less than 1 degree, and even of less than 10 minutes. Thisultra low friction level can be achieved with a ferrofluid bearing thatprovides a low friction interface between the magnet and supportstructure. A conductor, preferably a coil, is arranged with respect tothe magnet so that an electrical signal is generated in the conductorand coupled out of the system in response to the magnet moving on itssupport structure. The ferrofluid preferably has a viscosity less thanabout 5 centipoise, and in a particular embodiment comprises a lightmineral oil medium mixed with isoparaffinic acid.

[0009] In one embodiment, the magnet moves within an enclosure andproduces a moving magnetic field that generates an electrical signal ina surrounding conductive coil. An air flow path is provided betweenopposite sides of the magnet which it moves, preferably by the magnetoccupying less than the full interior cross-sectional area of theenclosure, to prevent a pressure buildup that could retard the magnetmovement. For a hand held device, the enclosure can be curved togenerally match the arc of an arm swing. The enclosure can be housed ina buoyant outer enclosure to that the unit generates an electricalsignal when the outer enclosure is floating and subjected to waveaction, or the unit can be suspended to generate an electrical signal inresponse to wind. Representative applications include battery chargingsystems, flashlights, environmental sensors, emergency transmitters andcellular telephones.

[0010] These and other features and advantages of the invention will beapparent to those skilled in the art from the following detaileddescription, taken together with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0011]FIGS. 1 and 2 are schematic diagrams illustrating the applicationof the invention to environmental sensor and emergency transmittingapplications, respectively;

[0012]FIG. 3 is a section view of an embodiment in which a magnet slidesalong a raceway formed in the enclosure;

[0013]FIG. 4 is a schematic diagram of the invention applied to aflashlight;

[0014]FIG. 5 is an elevation view illustrating a curved flashlight thatis operated in response to the user's hand motion while walking;

[0015]FIG. 6 is a simplified perspective view of an electrical generatorin accordance with the invention actuated in response to wave motion;

[0016]FIG. 7 is a simplified perspective view of an electrical generatorin accordance with the invention actuated in response to air motion;

[0017]FIG. 8 is a simplified plan view of a cellular telephone poweredin accordance with the invention;

[0018]FIG. 9 is an illustrative graph of the energy produced by anoscillating magnet system as a function of the static coefficient offriction between the magnet and its support structure;

[0019]FIG. 10 is a diagram illustrating the ultra low friction that canbe achieved with a new ferrofluid lubricant;

[0020]FIG. 11 is a sectional view of an embodiment with a magnet outsidea housing and a pickup coil inside; and

[0021]FIG. 12 is a graph of output voltage produced with the deviceshown in FIG. 11.

DETAILED DESCRIPTION OF THE INVENTION

[0022] The present invention provides an ultra low degree of frictionbetween a magnet and a support structure for the magnet, allowing foruseful generation of electricity from very slight movements of thesupport structure off a horizontal plane and/or movements in ahorizontal plane. For example, a walking motion or other normal motionssuch as turning, tapping, bowing, or even riding in a vehicle that issubject to vibration, can easily generate a useful amount of electricitywhen the support structure is held in the user's hand or in a shirtpocket, while slight off-horizontal movements due to wave or wind actioncan also be used for electrical generation.

[0023] To enable a highly sensitive response of the magnet to movementsof its support structure, ferrofluid bearings are preferably employed asan interface between the magnet and support structure. Ferrofluids aredispersions of finely divided magnetic or magnetizable particles,generally ranging between about 30 and 150 Angstroms in size, anddispersed in a liquid carrier. The magnetic particles are typicallycovered with surfactants or a dispersing agent. The surfactants assure apermanent distance between the magnetic particles to overcome the forcesof attraction caused by Van der Waal forces and magnetic interaction,and also provide a chemical composition on the outer layer of thecovered particles which is compatible with the liquid carrier and thechemicals in the surrounding environment. Ferrites and ferric oxidesemployed as magnetic particles offer a number of physical and chemicalproperties to the ferrofluid, including saturation magnetization,viscosity, magnetic stability, and chemical stability. Several types offerrofluids are provided by Ferrotec (USA) Corporation of Nashua, N.H. Asummary of patents related to the preparation of ferrofluids is providedin U.S. Pat. No. 6,056,889.

[0024] Ferrofluids have been used previously in electrically drivensystems. For example, U.S. Pat. No. 5,323,076 discloses a disk spindlemotor in which a ferrofluid lubricant is used as an alternative to ballbearings for a rotating electrically driven spindle. In U.S. Pat. No.5,452,520, ferrofluid bands provide bearings for a magnet that slideswithin an inclinometer, with movements of the magnet away from a neutralposition detected by a Hall element or coil, and used to energize coilsat each end of the device which restore the magnet to its neutralposition.

[0025] An effort has also been made to employ ferrofluids in thegeneration of electricity to power external systems. U.S. Pat. No.4,064,409 utilized the characteristic of ferrofluids experiencing rapidchanges in their magnetic properties with changing temperature, byplacing a magnet around a closed circuit ferrofluid system to create aself-pumping action of the ferrofluid through a solenoid that generateselectric power. However, this type of system requires an external heatsource and is not conducive to remote or portable operation.

[0026] Applicants have discovered a new way to utilize ferrofluids inthe generation of electrical energy used to power systems external tothe generator itself. This new approach is based upon the low frictioncharacteristics of ferrofluids, rather than their change in magneticproperties with temperature. A reciprocating system is provided in whicha magnet moves relative to a conductive coil to induce an emf in thecoil and thereby generate a current flow. With the use of a properlyselected ferrofluid lubricant for the magnet, an extremely lowcoefficient of friction is provided that allows the magnet to move andgenerate electricity in response to very slight tilting or translationmovements imparts to its enclosure. It is not necessary to vigorouslyshake the apparatus or hold it vertically, as in prior moving magnetgenerators.

[0027] The characteristics of the ferrofluid and magnet are related. Ifthe magnet has a relatively low magnetic field, a ferrofluid ofrelatively high magnetization should be used. The magnet's magneticfield will typically range from about 500-4,000 Gauss, and themagnetization of the ferrofluid from about 50-400 Gauss.

[0028] The ferrofluid's frictional coefficient is roughly related to itsviscosity (measured in centipoise (cp)), but not directly. For example,a ferrofluid with a viscosity of 300 cp has been found to have a staticfriction coefficient of about 0.015, the EFH1 ferrofluid from Ferrotec(USA) Corporation has a viscosity on the order of 6 cp and a staticfriction coefficient of about 0.002, but a water based ferrofluid with aviscosity of 5 cp has been found to have a static friction coefficientof about 0.01. The high friction coefficient for the somewhat lowerviscosity composition has been attributed to a surface tensionassociated with the water based solvent.

[0029] A preferred ferrofluid composition for the present invention hasa viscosity substantially less than 5 cp, actually less than 2 cp, andachieves an ultra low coefficient of static friction in the range of0.0008-0.0012. This is sensitive enough for a magnet on a beam to beginsliding when the beam is tilted only about 0.070 off horizontal. Thisand other suitable ferrofluid compositions are discussed in copendingpatent application Ser. No. ______, entitled “Mechanical Translator WithUltra Low Friction Ferrofluid Bearings”, filed on the same day as thepresent invention by applicant Jeffrey T. Cheung, and also assigned toInnovative Technology Licensing, LLC, the assignee of the presentinvention, the contents of which application are hereby incorporatedherein by reference. The composition comprises a mixture of one partFerrotec (USA) Corporation EFH1 light mineral oil ferrofluid, mixed withfrom two to four parts of isoparaffinic acid, stirred for 24 hours.Suitable sources of isoparaffinic acid are Isopar 6 and Isopar Mhydrocarbon fluids from Exxon Mobil Chemical Corp. Undiluted EFH1ferrofluid could also be used. Undiluted EFH1 composition has a greaterweight bearing capacity than the diluted version, but diluting thecomposition will retain sufficient weight bearing capability for mostapplications. Other ferrofluids with static friction coefficients up toabout 0.02 could also be used, such as Ferrotec (USA) Corporation typeEMG 805, a water based ferrofluid with a static friction coefficient ofabout 0.01 and a viscosity of about 5 cp, since the power outputachievable with a 0.01 static friction coefficient is still about 75%that achievable with a zero friction system. At present the EMG 805composition is considerably more expensive than the EFH1 composition andhas a somewhat lesser load bearing capability.

[0030]FIG. 1 illustrates the application of the invention to anenvironmental sensor. A movable permanent magnet 2 is housed within anonmagnetic enclosure 4, with magnets 6 and 8 at opposite ends of theenclosure in axial polar opposition to central magnet 2. Thus, the endsof the moving and end magnets which face each other are of like magneticpolarity so that the kinetic energy of the moving magnet is converted topotential energy as it approaches an end magnet, and then back tokinetic energy as it is repelled away from the end magnet. A ferrofluidwithin the enclosure is naturally attracted to the poles of magnet 2 toform beads 10, 12 around the end poles of the magnet. This provides anultra low friction lubricant that allows the magnet 2 to freely movewithin the enclosure, which provides a supporting structure for themagnet. The magnet will move relative to the enclosure in response toeither a tilting of the enclosure away from horizontal, or a horizontalmovement of the enclosure.

[0031] A conductive coil 14, typically copper, is wound around at leasta portion of the enclosure that is traversed by the magnet 2 in its pathbetween the end magnets 6 and 8. Movement of the magnet relative to itsenclosure generates a current in coil 14, due to the magnet's movingmagnetic field cutting the turns of the coil. The repulsive effect ofend magnets 6 and 8 limit the travel of moving magnet 2 with acushioning effect that prevents it from striking the hard end magnets.Since the magnetic repulsion force varies with 1/d⁴, where d is thedifference between two magnets, the repulsive force increases veryrapidly as the moving magnet approaches one of the end magnets.

[0032] Magnet 2 and enclosure 4 both preferably have generally circularcross-sections. The dimensions of the components are preferably selectedto leave a gap between the ferrofluid beads 10 and 12 and the upperenclosure wall, thereby preventing an air buildup on one side of thesliding magnet and a partial vacuum on the other side that couldotherwise develop and retard the magnet's movement. Alternatively, themagnet could be perforated to allow an air flow between its oppositesides if it is desired that (together with the ferrofluid bearings) itoccupy the full cross-sectional inner area of the enclosure.

[0033] A movement imparted to the enclosure 4 causes the magnet 2 toreciprocate back and forth between the end magnets 6, 8. Depending uponthe particular application, the enclosure movement can be a single axialmovement, reciprocating along a longitudinal axis, pivoting about acenter axis, rotational, or other more complex forms of movement. As themagnet 2 moves back and forth, it generates an AC current in the coil14. In the embodiment illustrated in FIG. 1, this current is rectifiedby a bridge circuit 16 and used to charge a battery 18, which provides apower source for an environmental sensor 20 that can sense one or moreenvironmental conditions such as temperature, pressure, gases, radiationor the like. To establish the sensor at a remote location, a transmitter22 can be provided to transmit information concerning the sensedcondition, with the transmitter also operated off of battery 18.Alternately, the sensor 20 can be operated in real time, directly fromthe output of coil 14 or bridge circuit 16, by eliminating the battery18.

[0034] The application of the invention to an emergency transmitter isillustrated in FIG. 2. The same ferrofluid libricated electricalgenerator as in FIG. 1 is illustrated, except in this embodiment the endmagnets have been replaced with springs 24, 26. This version provides agentler stop to the moving magnet, since the spring force increasesgenerally linearly rather than in proportion to 1/d⁴ as with endmagnets, but it has the disadvantage of physically contacting thereciprocating magnet 2 at each end of its travel and possibly damagingthe magnet through repeated contacts over time.

[0035] The coil output is connected to a rectifying bridge circuit 28,the output of which charges a battery 30 that powers an emergencytransmitter 32. Applications for this system include a wave-poweredgenerator for transmitting emergency signals at sea, and a wind-poweredsystem for land transmissions, illustrated respectively in FIGS. 6 and7.

[0036]FIG. 3 illustrates one possible configuration for the enclosure 4in which a shaped raceway 34 is provided in the wall of an otherwisecircular cross-sectional enclosure, with the magnet 2 dimensioned sothat it slides in the raceway and avoids lateral motion. This is usefulfor applications in which the enclosure experiences movements in thelateral direction, as well as in the plane of the magnet travel, helpingto confine the magnet to a longitudinal movement.

[0037] The enclosure 4 which provides a support structure for the magnetpreferably has a smooth, nonporous surface that does not absorb theferrofluid. Materials such as polycarbonates and glass are suitable,while Teflon® is not desirable because it tends to absorb theferrofluid.

[0038] The invention has many applications, a few of which areillustrated herein. FIG. 4 illustrates the invention as applied to ahand held flashlight. An electrical generator 36 as described above isprovided within a flashlight housing 38, with an illuminating bulb 40 atone end held to a bulb contact 42 and emitting light through atransparent plate 44 that can be screwed off to access the bulb. As withthe other embodiments described above, the generator 36 provides an ACoutput that is rectified by a bridge circuit 46 which charges a battery48 connected in circuit with the bulb contact 42. Again, the battery canbe eliminated if real time flashlight operation is desired, and in anyapplication of the invention the bridge circuit can be eliminated if itis desired to operate directly from an AC signal.

[0039]FIG. 5 illustrates a variation in which the longitudinal axis of aflashlight housing 38′ is curved along an arc, rather than straight;numerous other ergonometric designs could also be envisioned. Theflashlight would be held in a person's hand 46, with its curvaturedesigned to match the arc through which the person's hand swings whilewalking. This provides a smoother movement between the magnet and itsenclosure during a normal walking movement.

[0040] An electrical generator operated by wave action is illustrated inFIG. 6. This system is useful for powering an emergency transmitter, arepeater station for underwater cable, and for other marine applicationsrequiring an electrical power source that is not otherwise available. Inthe illustrated embodiment, a pair of buoyant tubular enclosures 48, 50are connected transverse to each other at their midsections. Eachenclosure houses an electrical generator as described above, and anyassociates electronics. When left to float in water 52, the twogenerators will be more stable and sensitive to wave action in differentdirections than a single generator. Their outputs can be combined toproduce a steadier supply of power than with a single generator. Otherconfigurations of multiple enclosures or a single shaped enclosure couldalso be used, such as linear arrays, three-dimensional arrays, trianglesand other geometric shapes.

[0041]FIG. 7 illustrates a wind-powered device that is similar to themarine generator of FIG. 6, but is suspended in air and moved by thewind to generate electricity. A support structure 54 includes asuspension system 56 that suspends the apparatus in the air, where itcan be blown by the wind. Again, the electrical generation apparatus isillustrated as a pair of tubular electrical generators 58, 60 that aretransverse to each other and connected at their midsections, with theends of the tubes attached to the support structure. Wind vanes or otherembellishments can be added to increase the generator's profile and makeit more sensitive to wind. As the enclosures swings off-horizontal dueto wind action, the magnets they house move along the tubes to producean electrical output.

[0042]FIG. 8 illustrates the application of the invention to a cellulartelephone 62 that can be placed in a person's shirt pocket or belt clip;for purposes of simplification the coil or coils wound on the magnetenclosure 4 are not shown. A battery and associated rectifying circuitryas in the other applications for the invention described above would beprovided within the telephone housing.

[0043] The magnet enclosure 4 is supported within the cell phone 62 sothat it has a generally horizontal orientation when the phone is placeupright in the user's shirt pocket or held in a belt clip. The motionsensitivity achieved with the invention allows power outputs on theorder of 0.4 watts to be readily achieved with the movement accompanyinga normal walking motion, whereas a typical cell phone presently consumesan average power of about 0.2 watts. Thus, cell phones and like devicesconstitute an important application for the invention.

[0044] The invention has many other applications involving devices thatare hand held, portable or otherwise subject to motion. For example, anelectrical generator as described herein could be installed on the axleof an automobile or other vehicle to capture vibrations from thevehicle's movement, and used to generate electrical power for airpressure sensors embedded in the vehicle tires. The pressure informationcould be transmitted to a driver display to provide a warning of low orhigh pressure conditions.

[0045] The achievement of an ultra low friction interface between themoving magnet and the walls of its enclosure is an important aspect ofsuccessfully implementing the invention. FIG. 9 graphically illustratesthe relative amount of energy produced, on a normalized basis, as afunction of the static friction coefficient between the magnet and theenclosure, for a horizontally oriented enclosure subjected to movementstypical of being carried while walking. It can be seen that the outputenergy drops rapidly from a frictionless system to a very low level at astatic friction coefficient of 0.1, with a more gradual dropoff afterthat until no output is achieved with a coefficient greater than about0.2. With the use of ferrofluid bearings that preferably provide anultra low static friction coefficient of about 0.01 or less, theinvention is capable of near optimum energy outputs.

[0046] The ultra low friction achievable with specific ferrofluids isillustrated by FIG. 10. A magnet 64 is shown supported on a substrate66, which in turn is on a horizontal support surface 68. A ferrofluidbearing 70 provides an ultra low friction interface between the magnet64 and substrate 66. The magnet is shown oriented with its magnetic axis72 generally transverse to the substrate 66.

[0047] With the use of an appropriate ferrofluid 16, ultra low degreesof friction can be achieved between the magnet and substrate, making themagnet highly responsive to a tilting of the substrate or an appliedtranslational force applied to the magnet. The static frictioncoefficient was measured by raising one end of the substrate 66 off thehorizontal surface 68 until the magnet began to slide along thesubstrate, determining the substre's critical off-horizontal angle ofdisplacement at which sliding movement began, returning the substrate tohorizontal, lifting its other end until the magnet started to slide inthe opposite direction, determining the critical angle of displacementfrom horizontal for sliding to begin in that direction, and averagingthe two angles. With an EFH1/isoparaffinic acid mixture as describedabove, the magnet began to slide at an average angle of much less than 1degree, and even considerably less than 10 minutes. In fact, thecritical angle for displacement from a horizontal static position wasfound to be approximately 0.07 degree.

[0048] While several embodiments of the invention have been shown anddescribed, numerous additional variations and embodiments will occur tothose skilled in the art. For example, rather than moving the enclosureas illustrated, the enclosure could be held in place and the magnetmoved, such as by a piston. Also, instead of placing the magnet inside ahousing and winding the coil around the outside of the housing, theelements could be reversed with the coil inside the magnet. Thisvariation is illustrated in FIG. 11, in which a toroidal shaped magnet74 whose magnetic field is aligned with its axis slides freely over atube 76 on ferrofluidic bearings 78. An electrical coil 80 is locatedinside the tube. As the magnet slides over the tube in the vicinity ofthe coil, an electrical output is produced by the coil and detected byvoltmeter 82. This variation can be used by itself, or coupled with anadditional outer coil that surrounds the magnet.

[0049] The signal produced with one example of the FIG. 11 design isshown in FIG. 12. A 268 turn coil was placed inside a 1.054 cm outsidediameter, 0.762 cm inside diameter tube. The magnet was a ceramic diskwith a 1.27 cm diameter opening through its center, dropped from aheight of 40 cm. The resulting AC voltage output had a peak of about 160mV.

[0050] Accordingly, it is intended that the invention be limited only interms of the appended claims.

We claim:
 1. An energy conversion device for transforming mechanicalmovement into electrical energy, comprising: a coil, and a magneticassembly including a magnet disposed for reciprocable movement to createa moving magnetic field relative to said coil, said coil configured tocouple electrical energy out of said device upon relative movementbetween said magnet and coil, wherein said device has a critical angleof displacement from a horizontal static position of less than 1 degree.2. The energy conversion device of claim 1, wherein said critical angleis less than 10 minutes.
 3. The energy conversion device of claim 1,further comprising a ferrofluidic bearing supporting said magnet.
 4. Theenergy conversion device of claim 3, wherein said magnetic assemblyfurther includes a polymeric race enveloping said magnet.
 5. The energyconversion device of claim 1, suspended for movement upon application ofa perturbation force.
 6. The energy conversion device of claim 1, saidassembly including a sealed tube housing said magnet.
 7. An electricalgenerator, comprising: a conductor, a support structure, a magnetconstrained by said support structure for movement relative to saidconductor, and a ferrofluid disposed between said magnet and supportstructure to provide a low friction interface, said conductor arrangedwith respect to said magnet so that relative motion between the magnetand conductor generates an electrical signal in said conductor.
 8. Theelectrical generator of claim 7, further comprising a pair of endmagnets on opposite sides of, and opposing polarity to, said magnet tolimit said magnet's motion.
 9. The electrical generator of claim 7, saidsupport structure including a raceway for said magnet.
 10. Theelectrical generator of claim 7, wherein said support structure isarranged for said magnet to move in response to a generally horizontalmovement of the support structure.
 11. The electrical generator of claim7, wherein said support structure is arranged to be carried by a personand for said magnet to move in a reciprocating motion in response tomotion of the person.
 12. The electrical generator of claim 7, whereinsaid ferrofluid has a viscosity less than 5 centipoise.
 13. Theelectrical generator of claim 7, wherein said ferrofluid comprises alight mineral oil medium mixed with isoparaffinic acid.
 14. Theelectrical generator of claim 1, further comprising circuitry forcoupling energy from said conductor out of said generator.
 15. Anelectrical generator, comprising: a magnet constrained to move relativeto an enclosure, a ferrofluid disposed between said magnet and enclosureto provide a low friction interface, and a conductive coil disposed withrespect to said magnet so that movement of said magnet relative to thecoil generates an electrical signal in said coil.
 16. The electricalgenerator of claim 15, wherein said coil is disposed along a portion ofsaid enclosure which is traversed by said magnet's movement.
 17. Theelectrical generator of claim 15, wherein said magnet is arranged withrespect to said enclosure to provide an air flow path between oppositesides of the magnet when the magnet moves.
 18. The electrical generatorof claim 17, wherein said magnet is inside said enclosure and occupiesless than the full interior cross-sectional area of said enclosure,providing said air flow path around the periphery of said magnet. 19.The electrical generator of claim 15, wherein said enclosure isgenerally tubular.
 20. The electrical generator of claim 15, furthercomprising a pair of end magnets on opposite sides of, and opposingpolarity to, said magnet to limit said magnet's movement.
 21. Theelectrical generator of claim 15, wherein said support structure isarranged for said magnet to move relative to the support structure inresponse to a generally horizontal movement of the support structure.22. The electrical generator of claim 15, wherein said support structureis arranged to be carried by a person and for said magnet to move in areciprocating motion relative to the support structure in response tomotion of the person.
 23. The electrical generator of claim 22, whereinsaid enclosure is curved.
 24. The electrical generator of claim 15,wherein said enclosure is housed in a buoyant outer enclosure forrelative movement between said magnet and coil that generates anelectrical signal in said coil when said outer enclosure is floating ona liquid and subjected to wave action.
 25. The electrical generator ofclaim 15, further comprising a suspension system for suspending saidenclosure so that the enclosure moves and causes said magnet to generatean electrical signal in said coil in response to wind striking theenclosure.
 26. The electrical generator of claim 15, wherein saidferrofluid has a viscosity less than 5 centipoise.
 27. The electricalgenerator of claim 15, wherein said ferrofluid comprises a light mineraloil medium mixed with isoparaffinic acid.
 28. The electrical generatorof claim 15, further comprising circuitry for coupling energy from saidcoil out of said generator.
 29. A battery charging system, comprising: aconductor, a battery contact, a support structure, a magnet constrainedby said support structure for movement relative to said conductor, and aferrofluid disposed between said magnet and support structure to providea low friction interface, said conductor arranged with respect to saidmagnet so that relative movement between the magnet and conductorgenerates a battery charging signal in said conductor, said conductorconnected to supply said battery charging signal to said batterycontact.
 30. The battery charging system of claim 29, further comprisinga rectifying circuit, said conductor connected to supply said batterycharging signal to said battery contact through said rectifying circuit.31. The battery charging system of claim 19, wherein said ferrofluid hasa viscosity less than 5 centipoise.
 32. The battery charging system ofclaim 31, wherein said ferrofluid comprises a light mineral oil mediummixed with isoparaffinic acid.
 33. A battery charging system,comprising: a coil, a battery contact, and a magnetic assembly includinga magnet disposed for reciprocable movement to create a moving magneticfield relative to said coil, said coil configured to couple electricalenergy to said battery contact upon relative movement between saidmagnet and coil, wherein said assembly has a critical angle ofdisplacement from a horizontal static position of less than 1 degree.34. The battery charging system of claim 33, wherein said critical angleis less than 10 minutes.
 35. An electrically operated device,comprising: a housing arranged to be carried, an electrical contact insaid housing, a conductor, a support structure in said housing, a magnetconstrained by said support structure for movement relative to saidsupport structure, and a ferrofluid disposed between said magnet andsupport structure to provide a low friction interface, said conductorarranged with respect to said magnet so that relative movement betweenthe magnet and conductor generates an electrical signal in saidconductor, said conductor connected to supply said energizing signal tosaid contact.
 36. The device of claim 35, wherein said ferrofluid has aviscosity less than 5 centipoise.
 37. The device of claim 35, whereinsaid ferrofluid comprises a light mineral oil medium mixed withisoparaffinic acid.
 38. An electrically operated device, comprising: acoil, a housing arranged to be carried, an electrical contact in saidhousing, and a magnetic assembly in said housing including a magnetdisposed for reciprocable movement to create a moving magnetic fieldrelative to said coil, said coil configured to couple electrical energyto said contact upon relative movement between said magnet and coil,wherein said assembly has a critical angle of displacement from ahorizontal static position of less than 1 degree.
 39. The device ofclaim 38, wherein said critical angle is less than 10 minutes.
 40. Anenvironmental sensing system, comprising: an environmental sensorarranged to produce an output signal indicative of an environmentalcondition, a conductor, a support structure, a magnet contrained by saidsupport structure for movement relative to said support structure, and aferrofluid disposed between said magnet and support structure to providea low friction interface, said conductor arranged with respect to saidmagnet so that relative movement between the magnet and conductorgenerates an energizing signal for said sensor.
 41. The environmentalsensing system of claim 40, said sensor including a transmitterenergized by said energizing signal for transmitting a signal indicativeof said environmental condition.
 42. The environmental sensing system ofclaim 40, said sensor including a battery, said conductor connected tosupply said energizing signal to said battery as a battery chargingsignal.
 43. The environmental sensing system of claim 40, said conductorconnected to supply said energizing signal to energize said sensor inreal time.
 44. The environmental sensing system of claim 40, furthercomprising a rectifying circuit, said conductor connected to supply saidenergizing signal to said sensor through said rectifying circuit. 45.The environmental sensing system of claim 40, wherein said ferrofluidhas a viscosity less than 5 centipoise.
 46. The environmental sensingsystem of claim 40, wherein said ferrofluid comprises a light mineraloil medium mixed with isoparaffinic acid.
 47. An environmental sensingsystem, comprising: an environmental sensor arranged to produce anoutput signal indicative of an environmental condition, a coil, and amagnetic assembly including a magnet disposed for reciprocable movementto create a moving magnetic field relative to said coil, said coilconfigured to couple electrical energy to said sensor upon relativemovement between said magnet and coil, wherein said assembly has acritical angle of displacement from a horizontal static position of lessthan 1 degree.
 48. The environment sensing system of claim 47, whereinsaid critical angle is less than 10 minutes.
 49. An emergencytransmitting system, comprising: an emergency signal transmitter, aconductor, a support structure, a magnet constrained by said supportstructure for movement relative to said support structure, and aferrofluid disposed between said magnet and support structure to providea low friction interface, said conductor arranged with respect to saidmagnet so that relative movement between the magnet and conductorgenerates an energizing signal for said transmitter.
 50. The emergencytransmitting system of claim 49, said transmitter including a battery,said conductor connected to supply said energizing signal to saidbattery as a battery charging signal.
 51. The emergency transmittingsystem of calim 49, said conductor connected to supply said energizingsignal to energize said transmitter in real time.
 52. The emergencytransmitting system of claim 49, further comprising a rectifyingcircuit, said conductor connected to supply said energizing signal tosaid transmitter through said rectifying circuit.
 53. The emergencytransmitting system of claim 49, wherein said ferrofluid has a viscosityless than 5 centipoise.
 54. The emergency transmitting system of claim49, wherein said ferrofluid comprises a light mineral oil medium mixedwith isoparaffinic acid.
 55. An emergency transmitting system,comprising: an emergency signal transmitter, a coil, and a magneticassembly including a magnet disposed for reciprocable movement to createa moving magnetic field relative to said coil, said coil configured tocouple electrical energy to said transmitter upon relative movementbetween said magnet and coil, wherein said assembly has a critical angleof displacement from a horizontal static position of less than 1 degree.56. The emergency transmitting system of claim 55, wherein said criticalangle is less than 10 minutes.
 57. A cellular telephone system,comprising: a cellular telephone, a conductor, a support structureconnected to said cellular telephone, a magnet constrained by saidsupport structure for movement relative to said support structure, and aferrofluid disposed between said magnet and support structure to providea low friction interface, said conductor arranged with respect to saidmagnet so that relative movement between the magnet and conductorgenerates an energizing signal for said cellular telephone.
 58. Thecellular telephone system of claim 57, said transmitter including abattery, said conductor connected to supply said energizing signal tosaid battery as a battery charging signal.
 59. The cellular telephonesystem of claim 57, wherein said ferrofluid has a viscosity less than 5centipoise.
 60. The cellular telephone system of claim 57 wherein saidferrofluid comprises a light mineral oil medium mixed with isoparaffinicacid.
 61. A cellular telephone system, comprising: a cellular telephone,a coil, and a magnetic assembly including a magnet disposed forreciprocable movement to create a moving magnetic field relative to saidcoil, said coil configured to couple electrical energy to said cellulartelephone upon relative movement between said magnet and coil, whereinsaid assembly has a critical angle of displacement from a horizontalstatic position of less than 1 degree.
 62. The cellular telephone systemof claim 61, wherein said critical angle is less than 10 minutes.
 63. Amethod of generating electricity, comprising: providing a low frictionferrofluid bearing for a magnet, causing the magnet to move on saidbearing with a reciprocating motion, and using the magnet's motion togenerate electricity.
 64. The method of claim 63, wherein saidferrofluid has a viscosity less than 5 centipoise.
 65. The method ofclaim 63, wherein said ferrofluid comprises a light mineral oil mediummixed with isoparaffinic acid.
 66. A method of generating electricity,comprising: providing a magnetic assembly that includes a magnetdisposed for reciprocable movement, and has a critical angle ofdisplacement from a horizontal static position of less than 1 degee,causing the magnet to move relative to a coil with a reciprocatingmotion to create a reciprocating magnetic field, and generating anelectrical signal in said coil with said magnetic field.
 67. The methodof claim 66, wherein said critical angle is less than 10 minutes.